Production method for carbon nanotubes

ABSTRACT

The invention shows a production method for carbon nanotubes. The production method comprises a first step of feeding at least one kind of gas-phase catalyst into a first chamber, the at least one kind of gas-phase catalyst being formed from an iron family element-containing substance and a halogen-containing substance that are contained in a first liquid; and a second step of forming the carbon nanotubes from a carbon source fed into the first chamber using a catalyst generated based on the gas-phase catalyst existing in the first chamber, wherein the first step includes vaporization of the first liquid, and the first liquid does not contain the carbon source.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the prioritybenefit of U.S. patent application Ser. No. 14/914,628, filed on Feb.25, 2016, now pending. The prior U.S. patent application Ser. No.14/914,628 is a 371 application of the international PCT applicationserial no. PCT/JP2014/072652, filed on Aug. 28, 2014, which claims thepriority benefit of Japan application no. 2013-177235, filed on Aug. 28,2013. The entirety of each of the above-mentioned patent applications ishereby incorporated by reference herein and made a part of thisspecification.

TECHNICAL FIELD

The present invention relates to a production method for carbonnanotubes.

As used herein, the “carbon nanotube array” (also referred to as a “CNTarray” herein) is a kind of a synthetic structure of a plurality ofcarbon nanotubes (also referred to as “CNT” herein) (hereinafter, theindividual shape of CNT giving such a synthetic structure will bereferred to as a “primary structure” while the above synthetic structuremay also be referred to as a “secondary structure”), and means anaggregate of CNT in which a plurality of CNT grow so as to be orientedin a predetermined direction (specific one example may be a directionsubstantially parallel to one normal line of a plane of a substrate)with regard to at least part of a major axis direction. The “growthheight” as used herein refers to a length (height) of a CNT array grownfrom a substrate in the direction parallel to the normal line of thesubstrate in a state in which the CNT array is attached on thesubstrate.

In the present description, a structure having a configuration in whicha plurality of CNT are entangled to each other will be referred to as a“CNT entangled body,” in which the structure is formed by continuouslydrawing the plurality of CNT from the CNT array by taking part of CNT ofthe CNT array to pull the CNT so as to be separated from the CNT array(work therefor herein will be also referred to as “spinning” after workfor producing threads from fibers as related to a conventional art).

BACKGROUND ART

CNT have a specific configuration of having an outside surface formed ofgraphene, and therefore application in various fields is expected as afunctional material and also as a structural material. Specifically, CNThave excellent characteristics, such as high mechanical strength, lightweight, satisfactory electrical conduction characteristics, satisfactoryheat characteristics such as heat resistance and heat conductivity, highresistance to chemical corrosion, and satisfactory field emissioncharacteristics. Accordingly, the use of CNT conceivably includes alightweight and high strength wire, a probe of a scanning probemicroscope (SPM), a cold cathode of a field emission display (FED), anelectrically conductive resin, a high strength resin, acorrosion-resistant resin, a wear-resistant resin, a highly lubricatingresin, electrodes of a secondary battery and fuel cell, an interlayerwiring material for LSI, and a biosensor.

As one of production methods for CNT, Patent Literature No. 1 disclosesa method comprising: preliminarily forming a solid-phase metal catalystlayer on a surface of a substrate by means of sputtering and the like,such as by vapor-depositing a thin film of a metallic material;disposing the substrate provided with the solid-phase metal catalystlayer in a reactor; forming catalyst particles from the metal catalystlayer to be growth nuclei on the substrate; and feeding a hydrocarbongas into the reactor to form a CNT array on the substrate. Hereinafter,the method comprising: forming the solid-phase catalyst particles as thegrowth nuclei on the substrate as described above; and feeding ahydrocarbon-based material into the reactor, in which the substrateprovided with the solid-phase catalyst particles is disposed, to producea CNT array will be referred to as a solid-phase catalysis process.

As a method for highly efficiently producing a CNT array by thesolid-phase catalysis process, Patent Literature No. 2 discloses amethod of feeding a material gas that contains carbon and no oxygen, acatalyst activator that contains oxygen, and an atmospheric gas, whilemeeting predetermined conditions so that they are brought into contactwith a solid-phase catalyst layer.

Another method is also disclosed which produces a CNT array in adifferent manner from that of the method described above. Morespecifically, Patent Literature No. 3 discloses a method comprising:sublimating iron chloride; using the sublimated iron chloride as aprecursor to form a catalyst to be growth nuclei on a substrate; andusing the catalyst to form a CNT array. This method is substantiallydifferent from the arts as disclosed in Patent Literature Nos. 1 and 2in that a halogen-containing substance in gas-phase is used as acatalyst precursor and this substance is used to form a catalyst. In thepresent description, the production method for a CNT array as disclosedin Patent Literature No. 3 will also be referred to as a gas-phasecatalysis process.

CITATION LIST Patent Literature

Patent Literature No. 1: JP 2004-107196 A

Patent Literature No. 2: JP 4803687 B

Patent Literature No. 3: JP 2009-196873 A

DISCLOSURE OF INVENTION Technical Problem

In the production method for a CNT array by such a gas-phase catalysisprocess, the action of the catalyst may be different, as caused bydifference in the forming process of the catalyst, from the productionmethod for a CNT array by the above solid-phase catalysis process.Therefore, the solid-phase catalysis process and the gas-phase catalysisprocess are considered to be substantially different production methodsfor a CNT array. Accordingly, when producing CNT having various primarystructures and secondary structures by the gas-phase catalysis process,a variety of approaches can be provided to improve the productivitybased on the production method being the gas-phase catalysis process.

The present invention provides a means capable of improving theproduction controllability of CNT to be produced by the above gas-phasecatalysis process.

Solution to Problem

The present invention is as described below.

(1) A production method for carbon nanotubes, comprising: a first stepof feeding at least one kind of gas-phase catalyst into a first chamber,the at least one kind of gas-phase catalyst being formed from an ironfamily element-containing substance and a halogen-containing substancethat are contained in a first liquid; and a second step of forming thecarbon nanotubes from a carbon source fed into the first chamber using acatalyst generated based on the gas-phase catalyst existing in the firstchamber, wherein the first step includes vaporization of the firstliquid, and the first liquid does not contain the carbon source.(2) The production method according to the above (1), wherein: the firststep includes allowing a substrate disposed in the first chamber toexist in an atmosphere including the gas-phase catalyst; and the secondstep includes forming the carbon nanotubes in an array-like form on abase surface of the substrate.(3) The production method according to the above (2), wherein the carbonsource is fed into the first chamber in a state in which the gas-phasecatalyst exists in the first chamber via the first step.(4) The production method according to any one of the above (1) to (3),wherein a temperature of the substrate in the first step is lower than atemperature of the substrate in the second step.(5) The production method according to the above (1), wherein the carbonnanotubes are formed as a generated substance by a gas-phase flowreaction.(6) The production method according to any one of the above (1) to (5),wherein an iron family element contained in the iron familyelement-containing substance includes iron.(7) The production method according to any one of the above (1) to (6),wherein the vaporization of the first liquid is performed outside thefirst chamber, and a vapor of the first liquid is fed into the firstchamber from outside of the first chamber.(8) The production method according to any one of the above (1) to (7),wherein the iron family element-containing substance contained in thefirst liquid includes an iron-methanol complex.

Advantageous Effects of Invention

According to the production method for CNT of the present invention, itbecomes easy to feed the gas-phase catalyst into the first chamber.Therefore, when the CNT are produced by the gas-phase catalysis process,it is expected to make easy to control the generation amount and thestructural properties (both the primary and secondary structures) of theCNT.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing schematically showing a configuration of aproduction apparatus for a CNT array according to a first embodiment ofthe present invention.

FIG. 2 is a drawing schematically showing a configuration of a gas-phasecatalyst feed device of the production apparatus shown in FIG. 1.

FIG. 3 is a drawing schematically showing a configuration of an exampleof a production apparatus for a CNT array according to a secondembodiment of the present invention.

FIG. 4 is a drawing schematically showing a configuration of anotherexample of a production apparatus for a CNT array according to thesecond embodiment of the present invention.

FIG. 5 is an image showing CNT that constitute a CNT array.

FIG. 6 is a graph showing an outer diameter distribution of CNT thatconstitute a CNT array.

FIG. 7 is an image showing a state in which a CNT entangled body isproduced by spinning a CNT array.

FIG. 8 is an enlarged image of part of a CNT entangled body obtainedfrom a CNT array.

FIG. 9 is an image when observing a CNT array produced by a productionmethod according to Example 1.

FIG. 10 is an image when observing a CNT array produced by a productionmethod according to Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below.

1. Production Apparatus for CNT Array

A production apparatus for a CNT array according to a first embodimentof the present invention will be described with reference to thedrawings.

FIG. 1 is a drawing schematically showing a configuration of aproduction apparatus used for a production method for a CNT arrayaccording to the first embodiment of the present invention.

As shown in FIG. 1, production apparatus 10 for a CNT array is providedwith electric furnace 12. Electric furnace 12 takes on a substantiallycylindrical shape that extends along predetermined direction A(direction in which a material gas flows). Inside electric furnace 12,reaction vessel pipe 14 as a first chamber having a growth region thatis a region in which CNT are formed is passed through. Reaction vesselpipe 14 is a substantially cylindrically-shaped member formed of aheat-resistant material such as quartz, has an outside diameter smallerthan an outside diameter of electric furnace 12, and extends alongpredetermined direction A. In FIG. 1, substrate 28 provided with a basesurface that is a surface on which a CNT array grows is disposed in thegrowth region of reaction vessel pipe 14. That is, the growth region inproduction apparatus 10 for a CNT array includes a region in whichsubstrate 28 in reaction vessel pipe 14 is disposed.

Electric furnace 12 is provided with heater 16 and thermocouple 18. Inproduction apparatus 10 for a CNT array, heater 16 and thermocouple 18constitute a first temperature adjustment device. Heater 16 is disposedso as to surround a predetermined region (in other words, apredetermined region of substantially cylindrically-shaped reactionvessel pipe 14 in an axial direction, and hereinafter, also referred toas a “heating region”) in predetermined direction A of reaction vesselpipe 14 to generate heat for raising a temperature of an atmosphere inthe pipe in the heating region of reaction vessel pipe 14. Thermocouple18 is disposed in the vicinity of the heating region of reaction vesselpipe 14 inside electric furnace 12 to allow output of an electricalsignal that represents a temperature associated with a temperature ofthe atmosphere in the pipe in the heating region of reaction vessel pipe14. Heater 16 and thermocouple 18 are electrically connected to controldevice 20.

To the upstream side (in FIG. 1, to one end at the left side) ofreaction vessel pipe 14 in predetermined direction A, feed device 22 isconnected. Feed device 22 is provided with raw material gas feed device30, first gas-phase material feed device 31, gas-phase co-catalyst feeddevice 32, and auxiliary gas feed device 33. Feed device 22 iselectrically connected to control device 20, and also electricallyconnected to each feed device of feed device 22.

Raw material gas feed device 30 (first feed device) can feed, into theinside of reaction vessel pipe 14 (in particular, to the growth region),a carbon compound (for example, hydrocarbon such as acetylene) thatserves as a raw material of CNT constituting the CNT array, i.e. a rawmaterial gas that contains a carbon source. A flow rate of feeding theraw material gas from raw material gas feed device 30 can be regulatedusing a publicly known flow rate regulating instrument such as massflow.

First gas-phase material feed device 31 can feed first gas-phasematerial G, which is obtained by vaporization of first liquid Laccommodated in first gas-phase material feed device 31, into the insideof reaction vessel pipe 14. As used herein, the “vaporization” meansboth of causing a substance contained in first liquid L to be in agas-phase state and forming an aerosol of first liquid L. Firstgas-phase material G contains a gas-phase catalyst originated from firstliquid L or a precursor of the gas-phase catalyst, and therefore firstgas-phase material feed device 31 can feed the gas-phase catalyst intothe inside of reaction vessel pipe 14 (in particular, to the growthregion). As used herein, the “gas-phase catalyst” means a collectiveterm of a substance that is a halogen-containing catalyst precursor andthat can be in a gas-phase state in the growth region of the reactionvessel pipe 14 and a suspended substance that is formed based on thehalogen-containing catalyst precursor. At least part of substances thatconstitute the gas-phase catalyst attaches on the base surface ofsubstrate 28, and at least part of catalysts that contribute toformation of CNT, in the present embodiment formation of a CNT array, isformed based on the attached substances.

As shown in FIG. 2, first gas-phase material feed device 31 has a unitstructure as will be described below. That is, first gas-phase materialfeed device 31 is provided with feed unit chamber 31A that canaccommodate first liquid L composed of at least one kind of a liquidthat contains a gas-phase catalyst and a liquid that contains aprecursor of the gas-phase catalyst and a feed unit temperatureadjustment device that can adjust the temperature of first liquid L infeed unit chamber 31A. In FIG. 2, the feed unit temperature adjustmentdevice is composed of heater 31B (part of the first vaporization device)and a temperature measurement device such as a thermocouple not shown.

First gas-phase material feed device 31 is provided with first liquidfeed device 31C that can feed first liquid L into feed unit chamber 31A.First liquid L is adjusted to a predetermined temperature by the feedunit temperature adjustment device (including heater 31B and the like)in feed unit chamber 31A thereby to be vaporized. Thus, in firstgas-phase material feed device 31, the feed unit temperature adjustmentdevice represents a feed unit vaporization device that can form firstgas-phase material G by vaporizing first liquid L. First gas-phasematerial feed device 31 is provided with discharge device 31D that candischarge first gas-phase material G in feed unit chamber 31A outsidethe feed unit chamber 31A. In FIG. 1, the destination of first gas-phasematerial G is inside of reaction vessel pipe 14, and first gas-phasematerial G is fed into reaction vessel pipe 14 from first gas-phasematerial feed device 31. First liquid feed device 31C and dischargedevice 31D may be provided with means for adjusting the amount of asubstance that passes therethrough.

When first gas-phase material G contains a gas-phase catalyst originatedfrom first liquid L, the gas-phase catalyst is fed to the growth regionin reaction vessel pipe 14. On the other hand, when first gas-phasematerial G contains a precursor of the gas-phase catalyst originatedfrom first liquid L, the gas-phase catalyst is formed from the precursorof the gas-phase catalyst, and the formed gas-phase catalyst is fed tothe growth region in reaction vessel pipe 14.

In first gas-phase material feed device 31 shown in FIG. 1, the feedunit temperature adjustment device represents a feed unit vaporizationdevice, and the feed unit temperature adjustment device vaporizes firstliquid L to generate the first gas-phase material, but the presentinvention is not limited thereto. For example, the feed unitvaporization device may be provided with a mechanism that regulates thepressure in feed unit chamber 31A, and the pressure in feed unit chamber31A may be reduced to vaporize first liquid L, or the feed unitvaporization device may be provided with a mechanism that feeds a gasinto first liquid L in feed unit chamber 31A, and an inert gas orhydrogen may be fed into (bubbled in) first liquid L to vaporize firstliquid L. In an alternative embodiment, the feed unit vaporizationdevice may be provided with a mechanism that increases the pressure offirst liquid L in feed unit chamber 31A and fine pores that can sprayfirst liquid L outside feed unit chamber 31A, and first liquid L may besprayed from the fine pores to vaporize.

First gas-phase material feed device 31 may have an exhaust system(pressure adjustment device) that can regulate the pressure in feed unitchamber 31A, and may also have a gas feed system (gas feed device) thatallows a gas to be fed into feed unit chamber 31A. Having such anexhaust system and/or gas feed system may make it easy to vaporize firstliquid L.

Gas-phase co-catalyst feed device 32 can feed a gas-phase co-catalystinto reaction vessel pipe 14 (in particular, to the growth region). Thegas-phase co-catalyst will be described later. The flow rate of feedingthe gas-phase co-catalyst from gas-phase co-catalyst feed device 32 canbe regulated using the publicly known flow rate regulating instrumentsuch as the mass flow.

Auxiliary gas feed device 33 allows feed of a gas other than the aboveraw material gas, first gas-phase material and gas-phase co-catalyst,for example, an inert gas such as argon (such a gas herein isgenerically referred to as an “auxiliary gas”) into reaction vessel pipe14 (in particular, to the growth region). The flow rate of feeding theauxiliary gas from auxiliary gas feed device 33 can be regulated usingthe publicly known flow rate regulating instrument such as the massflow.

To the other end at the downstream side (right side in FIG. 1) ofreaction vessel pipe 14 in predetermined direction A, pressureregulating valve 23 (part of the pressure adjustment device) and exhaustdevice 24 (also part of the pressure adjustment device) are connected.Pressure regulating valve 23 allows regulation of the pressure inreaction vessel pipe 14 by varying a degree of opening and closing ofthe valve. Exhaust device 24 performs vacuum exhaust of the inside ofreaction vessel pipe 14. Specific types of exhaust device 24 are notparticularly limited, and a rotary pump, oil diffusion pump, mechanicalbooster, turbomolecular pump, cryopump or the like can be used alone orin combination therewith. Pressure regulating valve 23 and exhaustdevice 24 are electrically connected to control device 20. In addition,reaction vessel pipe 14 is provided therein with pressure gauge 13 formeasuring the internal pressure thereof. Pressure gauge 13 iselectrically connected to control device 20 to allow output of anelectrical signal that represents the internal pressure of reactionvessel pipe 14 to control device 20.

As described above, control device 20 is electrically connected toheater 16, thermocouple 18, feed device 22, pressure gauge 13, pressureregulating valve 23 and exhaust device 24 to be input with theelectrical signals output from the devices or the like, and based on theinput electrical signals, to control operation of the devices or thelike. Examples of specific operation of control device 20 will bepresented below.

Control device 20 allows input of the electrical signal output fromthermocouple 18 and related to the internal temperature of reactionvessel pipe 14, and to heater 16, allows output of a control signalrelated to operation of heater 16 as determined based on the electricalsignal. Heater 16 to which the control signal from the control device isinput allows operation for increasing or decreasing an amount ofproduced heat to vary the internal temperature in the heating region ofreaction vessel pipe 14, based on the control signal.

Control device 20 allows input of an electrical signal output frompressure gauge 13 and related to the internal pressure in the heatingregion of reaction vessel pipe 14, and to pressure regulating valve 23and exhaust device 24, allows output of a control signal as related tooperation of pressure regulating valve 23 and exhaust device 24 asdetermined based on the electrical signal. Pressure regulating valve 23and exhaust device 24 to which the control signal from control device 20is input allow operation of varying a degree of opening of pressureregulating valve 23, and/or varying the exhausting capability of exhaustdevice 24, and the like, based on the control signal.

According to a preset timetable, control device 20 allows, to eachdevice, output of a control signal for controlling operation of eachdevice or the like. For example, control device 20 allows, to feeddevice 22, output of a control signal for determining start and stop offeeding a substance from each of raw material gas feed device 30, firstgas-phase material feed device 31, gas-phase co-catalyst feed device 32and auxiliary gas feed device 33 of gas feed device 22, and the flowrate of feed thereof. Gas feed device 22 to which the control signal isinput, according to the control signal, allows operation of each feeddevice to start or stop feed of each substance such as the raw materialgas into reaction vessel pipe 14.

Control device 20 can control operation of each part that constitutesfirst gas-phase material feed device 31. More specifically, based on theelectrical signal from the temperature measurement device such as athermocouple of first gas-phase material feed device 31, control device20 can output a control signal as related to operation of heater 31B.Heater 31B, to which the control signal is input, varies the temperatureof first liquid L in feed unit chamber 31A in accordance with thecontrol signal. This variation of temperature can adjust the generationamount of first gas-phase material G. Control device 20 can output acontrol signal as related to operation of first liquid feed device 31C.First liquid feed device 31C, to which the control signal is input,varies the feed amount of first liquid L into feed unit chamber 31A inaccordance with the control signal. Control device 20 can output acontrol signal as related to operation of discharge device 31D.Discharge device 31D, to which the control signal is input, can adjustthe timing and amount of discharging first gas-phase material G outsidefeed unit chamber 31A, i.e. feeding first gas-phase material G intoreaction vessel pipe 14 in FIG. 1, in accordance with the controlsignal. When first gas-phase material feed device 31 is provided withadditional exhaust system and/or gas feed system as described above,control device 20 can output control signals as related to operationsthereof.

A production apparatus for a CNT array according to a second embodimentof the present invention will be described with reference to thedrawings. FIG. 3 is a drawing schematically showing a configuration of aproduction apparatus used for a production method for a CNT arrayaccording to the second embodiment of the present invention. As shown inFIG. 3, production apparatus 50 for a CNT array according to the secondembodiment of the present invention has a common basic configurationwith that of production apparatus 10 for a CNT array according to thefirst embodiment of the present invention as shown in FIG. 1 except thatfeed device 22 is provided with a heat-resistant tray 29 that is locatedin electric furnace 12 and can accommodate first liquid L therein, assubstitute for first gas-phase material feed device 31 provided in feeddevice 22, and that first liquid L is accommodated in heat-resistanttray 29 in reaction vessel pipe 14.

In such a configuration of production apparatus 50 for a CNT arrayaccording to the second embodiment of the present invention, thevaporization of first liquid L is performed in reaction vessel pipe 14.A gas-phase catalyst contained in first gas-phase material G obtained byvaporization of first liquid L or a gas-phase catalyst formed from firstgas-phase material G diffuses in reaction vessel pipe 14 to reach thegrowth region. In FIG. 3, heater 16 can adjust the temperature ofsubstrate 28 disposed in reaction vessel pipe 14 and the temperature offirst liquid L in heat-resistant tray 29. Thus, in production apparatus50 for a CNT array according to the second embodiment, heater 16 andthermocouple 18 constitute a vaporization device for first liquid L.

As in production apparatus 50 for a CNT array according to the secondembodiment of the present invention, when the vaporization of firstliquid L is performed in reaction vessel pipe 14, the atmospheretemperature in reaction vessel pipe 14 can be controlled in a dividedmanner in reaction vessel pipe 14. For example, production apparatus 60for a CNT array shown in FIG. 4 is provided with a plurality ofthermocouples 18A and 18B, and heater 16 can control the temperature ina divided manner in the axial direction of reaction vessel pipe 14(upstream side and downstream side) based on the electrical signals fromrespective thermocouples.

Therefore, in the region at the upstream side (left side in FIG. 4) ofreaction vessel pipe 14, the upstream side (left side in FIG. 4) ofheater 16 can be operated based on the electrical signal fromthermocouple 18A thereby to adjust the temperature of first liquid L inheat-resistant tray 29.

In the region at the downstream side (right side in FIG. 4) of reactionvessel pipe 14, the downstream side (right side in FIG. 4) of heater 16can be operated based on the electrical signal from thermocouple 18Bthereby to adjust the temperature of the growth region in whichsubstrate 28 is disposed. According to such a structure, it is possibleto generate first gas-phase material G at the upstream side of reactionvessel pipe 14 while adjusting the temperature of the reaction region atthe downstream side of reaction vessel pipe 14.

A production apparatus for a CNT array according to an embodiment of thepresent invention may be provided with two or more structural featuresof the above production apparatuses 10, 50 and 60 for a CNT array. In anembodiment, a CNT apparatus may be provided with first gas-phasematerial feed device 31 so as to be capable of feeding first gas-phasematerial G into reaction vessel pipe 14 and may further be provided withheat-resistant tray 29 so that the vaporization of first liquid Ldisposed in reaction vessel pipe 14 can be carried out in reactionvessel pipe 14.

2. Production Method for CNT Array

A production method for a CNT array according to an embodiment of thepresent invention will be described. The production method for a CNTarray according to the present embodiment includes a first step and asecond step.

(1) First Step

The production method for a CNT array according to the presentembodiment includes a first step that feeds at least one kind ofgas-phase catalyst, which is formed from an iron familyelement-containing substance and a halogen-containing substance that arecontained in first liquid L, into the first chamber. Here, the firststep includes vaporization of first liquid L. This vaporization of firstliquid L may be performed outside reaction vessel pipe 14 as in the caseof using production apparatus 10 for a CNT array, or may also beperformed inside reaction vessel pipe 14 as in the case of usingproduction apparatus 50 or 60 for a CNT array. First gas-phase materialG, which is a vapor of first liquid L, contains a gas-phase catalyst ora precursor of the gas-phase catalyst, and therefore, by performing thefirst step, substrate 28 disposed in reaction vessel pipe 14 is allowedto exist in an atmosphere that includes the gas-phase catalyst.

Here, in the production method for a CNT array according to the presentembodiment, it is preferred that substrate 28 is provided with a basesurface that is a surface formed of a material including an oxide ofsilicon, at least as part of the surface of substrate 28.

The specific constitution of substrate 28 is not limited. The shapethereof is arbitrary, and may be a simple shape such as a flat plate ora cylinder, or may have a three-dimensional shape in which complicatedrecesses and projections are provided. Moreover, the entire surface ofthe substrate may be the base surface, or may be in a so-calledpatterned state in which only part of the surface of the substrate isthe base surface, and other parts are not.

The base surface is a surface formed of a material that contains anoxide of silicon, and the CNT array is formed on the base surface in thesecond step. Detail of the material constituting the base surface is notlimited as long as the material contains an oxide of silicon. Specificone example of the material constituting the base surface may be quartz(SiO₂). Specific other examples of the material constituting the basesurface include SiO_(x) (x≤2) which can be obtained such as bysputtering silicon in an oxygen-containing atmosphere. Specific stillanother example may be silicon-containing composite oxide. Specificexamples of an element other than silicon and oxygen that constitutesthe composite oxide include Fe, Ni and Al. Specific still anotherexample may be a compound in which a nonmetallic element such asnitrogen and boron is added to an oxide of silicon.

The material constituting the base surface may be identical with ordifferent from a material constituting substrate 28. To present specificexamples, specific examples include a case where the materialconstituting substrate 28 is formed of quartz and the materialconstituting the base surface is also formed of quartz, and a case wherethe material constituting substrate 28 is formed of a silicon substratebased essentially on silicon, and the material constituting the basesurface is formed of an oxide film thereof.

As described above, the first step includes: feeding the gas-phasecatalyst via first liquid L into reaction vessel pipe 14 using firstgas-phase material feed device 31 in production apparatus 10 or usingheat-resistant tray 29 in production apparatus 50 or 60; and allowingsubstrate 28 provided with the above base surface to exist in anatmosphere that includes the gas-phase catalyst. Any of productionapparatuses 10, 50 and 60 for a CNT array can be used to feed variouskinds of gas-phase catalysts into reaction vessel pipe 14 byappropriately selecting the kind of iron family element-containingsubstance and halogen-containing substance that are contained in firstliquid L.

The iron family element-containing material contained in first liquid Lis a substance that contains an iron family element (i.e. at least onekind of iron, cobalt, and nickel), and the specific composition thereofis not limited. Specific examples of the iron family element-containingmaterial include a coordinate compound having an iron family element asat least one of central metal elements, such as an iron-methanolcomplex, and ions of an iron family element. The iron familyelement-containing substance may be constituted of one kind of material,or may also be constituted of plural kinds of materials. In view of easyavailability, easy formation of CNT and the like, it is preferred thatthe iron family elements contained in the iron family element-containingsubstance include iron.

The halogen-containing substance contained in first liquid L is asubstance that contains halogen (i.e. at least one kind of fluorine,chlorine, bromine, and iodine), and the specific composition thereof isnot limited. Specific examples of the halogen-containing substanceinclude fluoride ions (F⁻), chloride ions (Cl⁻), bromide ions (Br⁻), andiodide ions (I⁻). The halogen-containing substance may be constituted ofone kind of substance, or may also be constituted of plural kinds ofsubstances. The iron family element-containing substance and thehalogen-containing substance may be in a state in which they interactwith each other in first liquid L. One example of such a compound may bechloride of an iron-methanol complex.

Solvent contained in first liquid L is not limited. The solvent may be aprotic polar solvent such as water and alcohol, an aprotic polar solventsuch as acetone and acetonitrile, or an apolar solvent such ascyclohexane and toluene. The composition of the solvent may beappropriately set in accordance with properties of the iron familyelement-containing substance and halogen-containing substance which arecontained in first liquid L.

The gas-phase catalyst according to the present embodiment includes areaction product of the iron family element-containing substance andhalogen-containing substance which are contained in first liquid L.Specific examples of the gas-phase catalyst include halide of an ironfamily element (also referred to as “iron family element halide”herein). Specific further examples of such iron family element halideinclude iron fluoride, cobalt fluoride, nickel fluoride, iron chloride,cobalt chloride, nickel chloride, iron bromide, cobalt bromide, nickelbromide, iron iodide, cobalt iodide, and nickel iodide. In the ironfamily element halide, different compounds may occasionally existaccording to valence of ion of the iron family element, such as iron(II)chloride and iron(III) chloride. The gas-phase catalyst may beconstituted of one kind of substance or plural kinds of substances.

The relationship between first liquid L and first gas-phase material Gis not particularly limited. In a specific example of a case in whichfirst liquid L is a methanol solution that contains the above chlorideof an iron-methanol complex, when first liquid L is heated to volatilizemethanol as the solvent, and as a result the generated solid-phase ironchloride sublimates, first gas-phase material G includes iron chloridewhich is one kind of the gas-phase catalyst. When the above first liquidL is vaporized such as by liquid mass flow, first gas-phase material Gis aerosol of first liquid L. From the methanol complex in this aerosolof first liquid L, iron chloride is generated in a similar manner to theabove case and sublimates to be one kind of the gas-phase catalyst. Inthis case, chloride of the iron-methanol complex in first liquid L isconsidered as a precursor of the gas-phase catalyst.

In addition to any of the above feed methods, another means may be usedto feed the gas-phase catalyst into reaction vessel pipe 14. To presenta specific example in such a case, when iron(II) chloride, anhydrous, asthe catalyst source is disposed inside the heating region of reactionvessel pipe 14 to sublimate the iron(II) chloride, anhydrous, by heatingthe inside of the heating region of reaction vessel pipe 14 andsimultaneously negatively pressurizing the inside, the gas-phasecatalyst including a vapor of the iron(II) chloride is allowed to existin reaction vessel pipe 14.

Pressure of the atmosphere in reaction vessel pipe 14 in the first step,specifically, in the growth region in which substrate 28 is disposed isnot particularly limited. The pressure may be the atmospheric pressure(about 1.0×10⁵ Pa) or a negative or positive pressure. When the insideof reaction vessel pipe 14 is adjusted to a negative pressure atmospherein the second step, the atmosphere is preferably adjusted to thenegative pressure also in the first step to shorten transition timebetween the steps. In a case where the inside of reaction vessel pipe 14is adjusted to the negative pressure atmosphere in the first step, thespecific total pressure in the atmosphere is not particularly limited.Specific examples include adjustment to 10⁻² Pa or more and 10⁴ Pa orless.

When first gas-phase material feed device 31 is used to feed thegas-phase catalyst, the temperature in the atmosphere in reaction vesselpipe 14 in the first step is not particularly limited. The temperaturemay be ordinary temperature (about 25° C.), and the atmosphere may beheated or cooled.

As will be described later, the growth region in reaction vessel pipe 14is preferably heated in the second step, and therefore the growth regionmay preferably be heated also in the first step to shorten thetransition time between the steps.

In addition to the above method, iron(II) chloride, anhydrous, may beused as the feed source for the gas-phase catalyst, this iron(II)chloride, anhydrous, may be heated to sublimate the iron(II) chloride,and a generated vapor of the iron(II) chloride may be introduced intoreaction vessel pipe 14 in which substrate 28 is disposed. Thesublimation temperature of iron(II) chloride is about 950 K in theatmospheric pressure (about 1.0×10⁵ Pa), but can be decreased byadjusting the atmosphere inside the heating region of reaction vesselpipe 14 to a negative pressure.

(2) Second Step

In the second step, the catalyst generated based on the gas-phasecatalyst existing in the first chamber is used to form CNT from thecarbon source contained in the raw material gas fed into the firstchamber. Specifically, at least one kind of gas-phase catalyst, which isformed from the iron family element-containing substance andhalogen-containing substance, is used as a catalyst precursor togenerate a catalyst on substrate 28, and the catalyst is used to formCNT from the carbon source.

Kinds of the raw material gas are not particularly limited, butordinarily, a hydrocarbon-based material is used and specific examplesinclude acetylene. The method for allowing the raw material gas to existin reaction vessel pipe 14 (particularly in the growth region) is notparticularly limited. As in production apparatuses 10, 50 and 60described above, the raw material gas may be allowed to exist by feedingthe raw material gas from raw material gas feed device 30, or a materialthat can generate the raw material gas may be allowed to previouslyexist inside reaction vessel pipe 14 to generate the raw material gasfrom the material and to diffuse the raw material gas in reaction vesselpipe 14, and thus the second step may be started. When the raw materialgas is fed from raw material gas feed device 30, the flow rate offeeding the raw material gas into reaction vessel pipe 14 is preferablycontrolled using a flow rate adjusting instrument. The flow rate of feedis ordinarily expressed in terms of a unit of sccm and 1 sccm means aflow rate of 1 mL per minute for gas converted under an environment of273 K and 1.01×10⁵ Pa. In the case of the production apparatuses 10, 50and 60 having the configurations as shown in FIGS. 1, 3 and 4, the flowrate of gas to be fed into reaction vessel pipe 14 is set up based on aninside diameter of reaction vessel pipe 14, pressure measured usingpressure gauge 13, and the like. Specific examples of a preferred flowrate of feeding an acetylene-containing raw material gas when thepressure by pressure gauge 13 is within 1×10² Pa or more and 1×10³ Pa orless include 10 sccm or more and 1,000 sccm or less, and in this case,the flow rate thereof is further preferably adjusted to 20 sccm or moreand 500 sccm or less, and particularly preferably, to 50 sccm or moreand 300 sccm or less.

As used herein, the “gas-phase co-catalyst” means a gas-phase componenthaving a function (hereinafter, also referred to as a “growth promotionfunction”) for enhancing the growth rate of a CNT array to be producedby the gas-phase catalysis process described above, and in a preferredembodiment, a gas-phase component having a function (hereinafter, alsoreferred to as a “function for improving spinning properties”) forfurther improving the spinning properties of the CNT array produced.Detail of the growth promotion function is not particularly limited.Specific components of the gas-phase co-catalyst are not particularlylimited as long as the components fulfill the growth promotion functiondescribed above, and preferably, also the function for improvingspinning properties, and specific examples include acetone.

The method for allowing the gas-phase co-catalyst to exist in reactionvessel pipe 14 (particularly in the growth region) in the second step isnot particularly limited. As in production apparatuses 10, 50 and 60described above, the gas-phase co-catalyst may be allowed to exist byfeeding the gas-phase co-catalyst from gas-phase co-catalyst feed device32. When the gas-phase co-catalyst is fed from gas-phase co-catalystfeed device 32, the flow rate of feeding the gas-phase co-catalyst intoreaction vessel pipe 14 is preferably controlled using the flow rateadjusting instrument. In an alternative embodiment, a material that cangenerate the gas-phase co-catalyst may be allowed to previously existinside reaction vessel pipe 14 to generate the gas-phase co-catalystfrom the material by means of heating, pressure reduction or the likeand to diffuse the gas-phase co-catalyst in reaction vessel pipe 14.

The total pressure in the atmosphere inside reaction vessel pipe 14 inthe second step is not particularly limited. The total pressure may bethe atmospheric pressure (about 1.0×10⁵ Pa) or a negative or positivepressure. The total pressure may be appropriately set up inconsideration of a composition (partial pressure ratio) of substancesexisting in reaction vessel pipe 14, or the like. To show specificexamples of a pressure range when the atmosphere inside the heatingregion in reaction vessel pipe 14 is adjusted to a negative pressure,the pressure range is adjusted to 1×10¹ Pa or more and 1×10⁴ Pa or less,preferably, 2×10¹ Pa or more and 5×10³ Pa or less, further preferably,5×10¹ Pa or more and 2×10³ Pa or less, and particularly preferably,1×10² Pa or more and 1×10³ Pa or less.

Temperature of the growth region in reaction vessel pipe 14 in thesecond step is not particularly limited as long as a CNT array can beformed on the base surface of substrate 28 using the raw material gasunder the condition in which an appropriate amount of the gas-phasecatalyst and the gas-phase co-catalyst, which is used as necessary,exists in the growth region. As described above, setting a loweredtemperature on the base surface of substrate 28 in the first step maycontribute to the formation of the catalyst on the base surface, inwhich case the temperature of the growth region in reaction vessel pipe14 in the second step may be changed to be higher than that in the firststep.

Temperature of the base surface in the second step may be controlled byadjusting the temperature of the growth region in reaction vessel pipe14. Temperature of the base surface of substrate 28 in the second stepis preferably heated to 8×10² K or higher. When the temperature of thebase surface of substrate 28 is 8×10² K or higher, interaction betweenthe gas-phase catalyst and gas-phase co-catalyst, which is used asnecessary, and the raw material gas is easily caused on the base surfaceto facilitate the growth of a CNT array on the base surface of substrate28. From a viewpoint of easily causing this interaction, the temperatureof the base surface in the second step is preferably heated to 9×10² Kor higher, more preferably 1.0×10³ K or higher, and particularlypreferably 1.1×10³ K or higher. The upper limit of the temperature ofthe base surface of substrate 28 in the second step is not particularlylimited, but when the temperature is excessively high, the materialconstituting the base surface and/or the material constituting thesubstrate (these materials may be or may not be identical) mayoccasionally lack in stability as solid, and therefore the upper limitis preferably set up in consideration of the melting point andsublimation temperature of these materials. When the load of thereaction vessel pipe is taken into consideration, the upper limit of thetemperature of substrate 28 is preferably adjusted to about 1.5×10³ K.

3. CNT Array

As one example of a CNT array produced by the production methodaccording to the present embodiment, as shown in FIG. 5, the CNT arrayhas a part having a configuration in which a plurality of CNT aredisposed so as to be oriented in a certain direction. When diameters ofthe plurality of CNT in the part are measured to determine adistribution thereof, as shown in FIG. 6, most of the diameters of theCNT are within a range of 20 to 50 nanometers. Diameters of CNT can bemeasured from an observed image obtained when observing CNT thatconstitute a CNT array, such as using an electron microscope.

The CNT array produced by the production method according to the presentembodiment can have the spinning properties. Specifically, the CNTconstituting the CNT array are taken and drawn (spun) in a direction inwhich the CNT are separated from the CNT array, and thus a structure(CNT entangled body) having the plurality of CNT entangled to each othercan be obtained. FIG. 7 is an image showing a state in which the CNTentangled body is formed from the CNT array, and FIG. 8 is an image inwhich part of the CNT entangled body is enlarged. As shown in FIG. 7,the CNT constituting the CNT array is continuously drawn, and thus theCNT entangled body is formed. Moreover, as shown in FIG. 8, the CNTconstituting the CNT entangled body is entangled to each other whilebeing oriented in a direction (spinning direction) in which the CNT isdrawn from the CNT array to form a connected body. A member having theCNT array and allowing formation of the CNT entangled body herein isalso referred to as a “spinning source member.”

4. CNT Entangled Body

The CNT entangled body obtained from the spinning source member can havevarious shapes. Specific one example may be a linear shape, and specificanother example may be a web shape. The linearly-shaped CNT entangledbody can be handled in a manner equivalent to that for fibers if twistis added when the spinning source member is drawn to obtain thelinearly-shaped CNT entangled body, and used also as electrical wiring.On the other hand, the web-shaped CNT entangled body can be directlyhandled in a manner similar to that for a nonwoven fabric.

The length of the CNT entangled body in the spinning direction is notparticularly limited, and needs to be appropriately set up according toan intended use. In general, the spinning length of 2 millimeters ormore allows application of the CNT entangled body to a part level suchas a contact part and an electrode. Moreover, in the linearly-shaped CNTentangled body, the degree of orientation of the CNT constituting thebody can be arbitrarily controlled by changing a spinning method fromthe spinning source member (examples thereof include varying the degreeof twist). Accordingly, the CNT entangled body in which the mechanicalcharacteristics or the electrical characteristics are different can beproduced by changing the spinning method from the spinning sourcemember.

If the degree of entanglement is decreased, the CNT entangled bodybecomes fine in the case of the linear shape, and thin in the case ofthe web shape. If the degree progresses, the CNT entangled body becomesdifficult to visually observe, and the CNT entangled body on theoccasion can be used as transparent fibers, transparent wiring, or atransparent web (transparent sheet-shaped member).

The CNT entangled body may consist only of CNT or may also be acomposite structure with any other material. As described above, the CNTentangled body has the configuration formed of the plurality of CNTbeing entangled to each other, and therefore a void exists among theplurality of entangled CNT in a manner similar to that for a pluralityof fibers constituting a nonwoven fabric. The composite structure can beeasily formed by introducing powder (specific examples include metalfine particles, inorganic particles such as particles of silica, andorganic particles such as particles of an ethylene-based polymer) intothe void portion thereof or impregnation with a liquid thereinto.

Moreover, the surface of the CNT constituting the CNT entangled body maybe modified. The outside surface of CNT is constituted of graphene, andtherefore the CNT entangled body is hydrophobic as is, but hydrophilictreatment is applied to the surface of the CNT constituting the CNTentangled body, and thus the CNT entangled body can be made hydrophilic.Specific one example of such a hydrophilization means may be platingtreatment. In the above case, the CNT entangled body obtained is formedinto the composite structure between the CNT and a plated metal.

5. Production Apparatus and Production Method for CNT Having Shape Otherthan Array Shape

CNT having a shape other than an array shape can be produced using anyof production apparatuses 10, 50 and 60 for a CNT array described above.For example, there can be formed an aggregate of curved CNT withoutanisotropy, i.e. CNT having a secondary structure that can function as athree-dimensional mesh as a result, in a state in which ends of each ofCNT are fixed on substrate 28 (such an aggregate of CNT will be referredto as a “CNT mesh” herein). The CNT mesh can be produced by adjustingproduction conditions in a similar method to the production method for aCNT array, i.e. a method of performing the first step (feed of thegas-phase catalyst) and the second step (feed of the carbon source)using any of production apparatuses 10, 50 and 60 for a CNT arraydescribed above. The CNT mesh can be used as a member having such afunction as that of bump of flip chip.

CNT can also be produced as a generated substance by a gas-phase flowreaction. Specifically, if the first step (feed of the gas-phasecatalyst) and the second step (feed of the carbon source) are carriedout in a state in which a substrate is not disposed in the growth regionwhere substrate 28 would be disposed when producing a CNT array,chemical interaction can be caused between the gas-phase catalystexisting in the growth region and the raw material gas containing thecarbon source to form CNT in the growth region as a generated substanceby a gas-phase flow reaction. During this operation, it is not easy forCNT grown in the growth region to grow to come close to one another tosuch an extent that the CNT have an array shape, so that CNT having lowanisotropy in shape can be obtained.

In view of more stably obtaining CNT as a generated substance by agas-phase flow reaction, the raw material gas may be fed prior tofeeding the gas-phase catalyst. That is, if the raw material gascontaining the carbon source is fed into reaction vessel pipe 14 toallow the carbon source to exist in reaction vessel pipe 14, and in thisstate the gas-phase catalyst is fed via first liquid L into reactionvessel pipe 14, the gas-phase catalyst fed into reaction vessel pipe 14can immediately interact with the carbon source to form CNT. In thiscase, the entire region in which the raw material gas exists in reactionvessel pipe 14 can be the growth region. Moreover, the growth region caninclude a region to which the gas-phase catalyst is fed in reactionvessel pipe 14. In view of more stably obtaining CNT as a generatedsubstance by a gas-phase flow reaction, predetermined direction A ofreaction vessel pipe 14 may be the downward direction in the verticaldirection.

The embodiments described above are set forth in order to facilitateunderstanding of the present invention, and not to limit the presentinvention. Therefore, each of the elements disclosed in the embodimentsdescribed above also includes all design modifications and equivalentsbelonging to the technical scope of the present invention.

EXAMPLES

The present invention will be further specifically described by way ofExamples and the like below, but the scope of the present invention isnot limited to the Examples and the like.

Example 1

(1) Preparation of First Liquid

A methanol solution of chloride of an iron-methanol complex was obtainedas a first liquid by dissolving 500 mg of iron powder into a mixture of3.0 mL of methanol (aqueous) and 1.0 mL of hydrochloric acid aqueoussolution (concentration: 35%).

(2) Production of CNT Array

A CNT array was produced using a production apparatus for a CNT arrayhaving the configuration shown in FIG. 3. A heat-resistant tray in whichthe above first liquid was accommodated was placed on the inside surfaceof a reaction vessel pipe as the first chamber.

As the substrate, a quartz plate (20 mm×5 mm×1 mm in thickness) wasprepared. Accordingly, in the present Example, all of the materialconstituting the base surface and the material constituting thesubstrate were quartz. The substrate was disposed in a portion locatedat the downstream side from the heat-resistant tray in the reactionvessel pipe, in a state where the quartz plate was placed on a quartzboat.

Inside of the reaction vessel pipe was evacuated to 1×10⁻¹ Pa or lessusing an evacuating device. Subsequently, the inside of the reactionvessel pipe was heated to 1.1×10³ K using a heater so that thetemperature of the heat-resistant tray and quartz plate would be about1.1×10³ K. The pressure in the tube was maintained at about 400 Pabecause the pressure in the reaction vessel pipe increased due to theheating.

In a state in which the temperature in the reaction vessel pipe was1.1×10³ K, the second step was carried out by feeding acetylene as theraw material gas from the raw material gas feed device at an amount tobe a flow rate of 190 sccm, and acetone as the gas-phase co-catalystfrom the gas-phase co-catalyst feed device at an amount to be a flowrate of 10 sccm, into the reaction vessel pipe for 10 minutes. Thepressure in the tube was maintained at about 400 Pa during the secondstep.

As a result, a CNT array (growth height: 700 μm) was obtained on thequartz plate as shown in FIG. 9.

Example 2

A methanol solution of iron chloride was obtained as a first liquid bydissolving 200 mg of iron(II) chloride, anhydrous, into 10 mL ofmethanol (anhydrous).

Thereafter, the first and second steps were carried out by performingthe same operation as in Example 1.

As a result, a CNT array was obtained on the quartz plate as shown inFIG. 10.

INDUSTRIAL APPLICABILITY

The CNT entangled body obtained from the CNT array produced by theproduction method for CNT according to the present invention is suitablyused as electrical wiring, a heater, a strain sensor, and a transparentelectrode sheet, for example. The CNT mesh and CNT without a specificsecondary structure produced by the production method for CNT accordingto the present invention are suitably used as an electrode material fora secondary cell.

The invention claimed is:
 1. A production method for carbon nanotubes,comprising: a first step of forming, from reaction of an iron familyelement-containing substance and a halogen-containing substance that arecontained in a first liquid, at least one kind of gas-phase catalystprecursor including a halide of an iron family element, and feeding theat least one kind of gas-phase catalyst precursor into a first chamber;and a second step of forming the carbon nanotubes from a carbon sourcefed into the first chamber using a catalyst generated based on thegas-phase catalyst precursor existing in the first chamber, wherein thefirst step includes vaporization of the first liquid, and the firstliquid does not contain the carbon source.
 2. The production methodaccording to claim 1, wherein: the first step includes allowing asubstrate disposed in the first chamber to exist in an atmosphereincluding the gas-phase catalyst precursor; and the second step includesforming the carbon nanotubes in an array-like form on a base surface ofthe substrate.
 3. The production method according to claim 2, whereinthe carbon source is fed into the first chamber in a state in which thegas-phase catalyst precursor exists in the first chamber via the firststep.
 4. The production method according to claim 1, wherein atemperature of the substrate in the first step is lower than atemperature of the substrate in the second step.
 5. The productionmethod according to claim 1, wherein the carbon nanotubes are formed asa generated substance by a gas-phase flow reaction.
 6. The productionmethod according to claim 1, wherein an iron family element contained inthe iron family element-containing substance includes iron.
 7. Theproduction method according to claim 1, wherein the vaporization of thefirst liquid is performed outside the first chamber, and a vapor of thefirst liquid is fed into the first chamber from outside of the firstchamber.
 8. The production method according to claim 1, wherein the ironfamily element-containing substance contained in the first liquidincludes an iron-methanol complex.